NDLI: TOAC Spin Labels in the Backbone of Alamethicin: EPR Studies in Lipid Membranes

Content Provider	PubMed Central
Author	Marsh, Derek Jost, Micha Cristina, Peggion Toniolo, Claudio
Copyright Year	2007
Abstract	Alamethicin is a 19-amino-acid residue hydrophobic peptide that produces voltage-dependent ion channels in membranes. Analogues of the Glu(OMe)7,18,19 variant of alamethicin F50/5 that are rigidly spin-labeled in the peptide backbone have been synthesized by replacing residue 1, 8, or 16 with 2,2,6,6-tetramethyl-piperidine-1-oxyl-4-amino-4-carboxyl (TOAC), a helicogenic nitroxyl amino acid. Conventional electron paramagnetic resonance spectra are used to determine the insertion and orientation of the TOACn alamethicins in fluid lipid bilayer membranes of dimyristoyl phosphatidylcholine. Isotropic 14N-hyperfine couplings indicate that TOAC8 and TOAC16 are situated in the hydrophobic core of the membrane, whereas the TOAC1 label resides closer to the membrane surface. Anisotropic hyperfine splittings show that alamethicin is highly ordered in the fluid membranes. Experiments with aligned membranes demonstrate that the principal diffusion axis lies close to the membrane normal, corresponding to a transmembrane orientation. Combination of data from the three spin-labeled positions yields both the dynamic order parameter of the peptide backbone and the intramolecular orientations of the TOAC groups. The latter are compared with x-ray diffraction results from alamethicin crystals. Saturation transfer electron paramagnetic resonance, which is sensitive to microsecond rotational motion, reveals that overall rotation of alamethicin is fast in fluid membranes, with effective correlation times <30 ns. Thus, alamethicin does not form large stable aggregates in fluid membranes, and ionic conductance must arise from transient or voltage-induced associations.
Related Links	http://dx.doi.org/10.1529/biophysj.106.092775
Ending Page	481
Page Count	9
Starting Page	473
File Format	PDF
ISSN	00063495
e-ISSN	15420086
Journal	Biophysical Journal
Issue Number	2
Volume Number	92
Language	English
Publisher	Biophysical Society
Publisher Date	2007-01-01
Access Restriction	Open
Rights Holder	Biophysical Society
Subject Keyword	Biophysics Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Biophysics

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